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Exponential Backoff GoDoc Build Status Coverage Status

This is a Go port of the exponential backoff algorithm from Google's HTTP Client Library for Java.

Exponential backoff is an algorithm that uses feedback to multiplicatively decrease the rate of some process, in order to gradually find an acceptable rate. The retries exponentially increase and stop increasing when a certain threshold is met.

Usage

See https://godoc.org/github.com/cenkalti/backoff#pkg-examples

Contributing

  • I would like to keep this library as small as possible.
  • Please don't send a PR without opening an issue and discussing it first.
  • If proposed change is not a common use case, I will probably not accept it.
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Documentation

Overview

    Package backoff implements backoff algorithms for retrying operations.

    Use Retry function for retrying operations that may fail. If Retry does not meet your needs, copy/paste the function into your project and modify as you wish.

    There is also Ticker type similar to time.Ticker. You can use it if you need to work with channels.

    See Examples section below for usage examples.

    Index

    Examples

    Constants

    View Source
    const (
    	DefaultInitialInterval     = 500 * time.Millisecond
    	DefaultRandomizationFactor = 0.5
    	DefaultMultiplier          = 1.5
    	DefaultMaxInterval         = 60 * time.Second
    	DefaultMaxElapsedTime      = 15 * time.Minute
    )

      Default values for ExponentialBackOff.

      View Source
      const Stop time.Duration = -1

        Stop indicates that no more retries should be made for use in NextBackOff().

        Variables

        View Source
        var SystemClock = systemClock{}

          SystemClock implements Clock interface that uses time.Now().

          Functions

          func Retry

          func Retry(o Operation, b BackOff) error

            Retry the operation o until it does not return error or BackOff stops. o is guaranteed to be run at least once. It is the caller's responsibility to reset b after Retry returns.

            If o returns a *PermanentError, the operation is not retried, and the wrapped error is returned.

            Retry sleeps the goroutine for the duration returned by BackOff after a failed operation returns.

            Example
            Output:
            
            

            func RetryNotify

            func RetryNotify(operation Operation, b BackOff, notify Notify) error

              RetryNotify calls notify function with the error and wait duration for each failed attempt before sleep.

              Types

              type BackOff

              type BackOff interface {
              	// NextBackOff returns the duration to wait before retrying the operation,
              	// or backoff.Stop to indicate that no more retries should be made.
              	//
              	// Example usage:
              	//
              	// 	duration := backoff.NextBackOff();
              	// 	if (duration == backoff.Stop) {
              	// 		// Do not retry operation.
              	// 	} else {
              	// 		// Sleep for duration and retry operation.
              	// 	}
              	//
              	NextBackOff() time.Duration
              
              	// Reset to initial state.
              	Reset()
              }

                BackOff is a backoff policy for retrying an operation.

                func WithMaxTries

                func WithMaxTries(b BackOff, max uint64) BackOff

                  WithMaxTries creates a wrapper around another BackOff, which will return Stop if NextBackOff() has been called too many times since the last time Reset() was called

                  Note: Implementation is not thread-safe.

                  type BackOffContext

                  type BackOffContext interface {
                  	BackOff
                  	Context() context.Context
                  }

                    BackOffContext is a backoff policy that stops retrying after the context is canceled.

                    func WithContext

                    func WithContext(b BackOff, ctx context.Context) BackOffContext

                      WithContext returns a BackOffContext with context ctx

                      ctx must not be nil

                      type Clock

                      type Clock interface {
                      	Now() time.Time
                      }

                        Clock is an interface that returns current time for BackOff.

                        type ConstantBackOff

                        type ConstantBackOff struct {
                        	Interval time.Duration
                        }

                          ConstantBackOff is a backoff policy that always returns the same backoff delay. This is in contrast to an exponential backoff policy, which returns a delay that grows longer as you call NextBackOff() over and over again.

                          func NewConstantBackOff

                          func NewConstantBackOff(d time.Duration) *ConstantBackOff

                          func (*ConstantBackOff) NextBackOff

                          func (b *ConstantBackOff) NextBackOff() time.Duration

                          func (*ConstantBackOff) Reset

                          func (b *ConstantBackOff) Reset()

                          type ExponentialBackOff

                          type ExponentialBackOff struct {
                          	InitialInterval     time.Duration
                          	RandomizationFactor float64
                          	Multiplier          float64
                          	MaxInterval         time.Duration
                          	// After MaxElapsedTime the ExponentialBackOff stops.
                          	// It never stops if MaxElapsedTime == 0.
                          	MaxElapsedTime time.Duration
                          	Clock          Clock
                          	// contains filtered or unexported fields
                          }

                            ExponentialBackOff is a backoff implementation that increases the backoff period for each retry attempt using a randomization function that grows exponentially.

                            NextBackOff() is calculated using the following formula:

                            randomized interval =
                                RetryInterval * (random value in range [1 - RandomizationFactor, 1 + RandomizationFactor])
                            

                            In other words NextBackOff() will range between the randomization factor percentage below and above the retry interval.

                            For example, given the following parameters:

                            RetryInterval = 2
                            RandomizationFactor = 0.5
                            Multiplier = 2
                            

                            the actual backoff period used in the next retry attempt will range between 1 and 3 seconds, multiplied by the exponential, that is, between 2 and 6 seconds.

                            Note: MaxInterval caps the RetryInterval and not the randomized interval.

                            If the time elapsed since an ExponentialBackOff instance is created goes past the MaxElapsedTime, then the method NextBackOff() starts returning backoff.Stop.

                            The elapsed time can be reset by calling Reset().

                            Example: Given the following default arguments, for 10 tries the sequence will be, and assuming we go over the MaxElapsedTime on the 10th try:

                            Request #  RetryInterval (seconds)  Randomized Interval (seconds)
                            
                             1          0.5                     [0.25,   0.75]
                             2          0.75                    [0.375,  1.125]
                             3          1.125                   [0.562,  1.687]
                             4          1.687                   [0.8435, 2.53]
                             5          2.53                    [1.265,  3.795]
                             6          3.795                   [1.897,  5.692]
                             7          5.692                   [2.846,  8.538]
                             8          8.538                   [4.269, 12.807]
                             9         12.807                   [6.403, 19.210]
                            10         19.210                   backoff.Stop
                            

                            Note: Implementation is not thread-safe.

                            func NewExponentialBackOff

                            func NewExponentialBackOff() *ExponentialBackOff

                              NewExponentialBackOff creates an instance of ExponentialBackOff using default values.

                              func (*ExponentialBackOff) GetElapsedTime

                              func (b *ExponentialBackOff) GetElapsedTime() time.Duration

                                GetElapsedTime returns the elapsed time since an ExponentialBackOff instance is created and is reset when Reset() is called.

                                The elapsed time is computed using time.Now().UnixNano().

                                func (*ExponentialBackOff) NextBackOff

                                func (b *ExponentialBackOff) NextBackOff() time.Duration

                                  NextBackOff calculates the next backoff interval using the formula:

                                  Randomized interval = RetryInterval +/- (RandomizationFactor * RetryInterval)
                                  

                                  func (*ExponentialBackOff) Reset

                                  func (b *ExponentialBackOff) Reset()

                                    Reset the interval back to the initial retry interval and restarts the timer.

                                    type Notify

                                    type Notify func(error, time.Duration)

                                      Notify is a notify-on-error function. It receives an operation error and backoff delay if the operation failed (with an error).

                                      NOTE that if the backoff policy stated to stop retrying, the notify function isn't called.

                                      type Operation

                                      type Operation func() error

                                        An Operation is executing by Retry() or RetryNotify(). The operation will be retried using a backoff policy if it returns an error.

                                        type PermanentError

                                        type PermanentError struct {
                                        	Err error
                                        }

                                          PermanentError signals that the operation should not be retried.

                                          func Permanent

                                          func Permanent(err error) *PermanentError

                                            Permanent wraps the given err in a *PermanentError.

                                            func (*PermanentError) Error

                                            func (e *PermanentError) Error() string

                                            type StopBackOff

                                            type StopBackOff struct{}

                                              StopBackOff is a fixed backoff policy that always returns backoff.Stop for NextBackOff(), meaning that the operation should never be retried.

                                              func (*StopBackOff) NextBackOff

                                              func (b *StopBackOff) NextBackOff() time.Duration

                                              func (*StopBackOff) Reset

                                              func (b *StopBackOff) Reset()

                                              type Ticker

                                              type Ticker struct {
                                              	C <-chan time.Time
                                              	// contains filtered or unexported fields
                                              }

                                                Ticker holds a channel that delivers `ticks' of a clock at times reported by a BackOff.

                                                Ticks will continue to arrive when the previous operation is still running, so operations that take a while to fail could run in quick succession.

                                                Example
                                                Output:
                                                
                                                

                                                func NewTicker

                                                func NewTicker(b BackOff) *Ticker

                                                  NewTicker returns a new Ticker containing a channel that will send the time at times specified by the BackOff argument. Ticker is guaranteed to tick at least once. The channel is closed when Stop method is called or BackOff stops.

                                                  func (*Ticker) Stop

                                                  func (t *Ticker) Stop()

                                                    Stop turns off a ticker. After Stop, no more ticks will be sent.

                                                    type ZeroBackOff

                                                    type ZeroBackOff struct{}

                                                      ZeroBackOff is a fixed backoff policy whose backoff time is always zero, meaning that the operation is retried immediately without waiting, indefinitely.

                                                      func (*ZeroBackOff) NextBackOff

                                                      func (b *ZeroBackOff) NextBackOff() time.Duration

                                                      func (*ZeroBackOff) Reset

                                                      func (b *ZeroBackOff) Reset()